A new class of soft contact lenses, water gradient contact lenses, have been developed and successfully introduced in the market. This new class of contact lenses is characterized by having a water-gradient structural configuration, an increase from 33% to over 80% water content from core to surface. This unique design delivers a highly-lubricious and extremely-soft lens surface. Such soft contact lenses can be produced according to a cost-effective approach that is described in U.S. Pat. No. 8,529,057 and involves a step of crosslinking and covalently attaching of a water-soluble highly-branched hydrophilic polymeric material onto lens surfaces to form surface gels.
According to U.S. Pat. No. 8,529,057, contact lenses having a water-gradient structural configuration and a soft and lubricious surface can be produced by forming an anchoring layer on each contact lens by dipping the contact lenses in a coating solution of a polyanionic polymer and then covalently attaching a water-soluble highly-branched hydrophilic polymeric material onto the anchoring layer directly in a lens package during autoclave. The water-soluble highly-branched hydrophilic polymeric material is prepared by partially reacting a polyamidoamine-epichlorohydrin (PAE) with a wetting agent, at various concentration ratio of PAE to the wetting agent and at a reaction temperature for a given reaction time, to achieve a desired lubricity of the surface gels while minimizing or eliminating surface defects (e.g., surface cracking, etc.). Although this new approach can provide hydrogel contact lenses having a water-gradient structural configuration, its applicability and advantages can be limited by the limited availability of hydrophilic copolymers having a better biocompatibility and having a versatility and controllability in the levels of reactivity and/or contents of reactive functional group towards the azetidinium groups of PAE.
Therefore, there is still a need for reactive hydrophilic polymers having a desired biocompatibility and a desired level of reactivity and/or contents of reactive functional groups for producing water-soluble highly-branched hydrophilic polymeric material useful for producing water gradient contact lenses.